A gas flowmeter measures a flow rate of a gas (fluid to be measured) in such a manner that an ultrasonic wave is propagated through a gas which flows in a measuring pipe provided to a middle portion of a gas flow passage. For example, the gas flowmeter measures a flow rate of a gas by making use of a propagation time of an ultrasonic wave or a propagation speed of an ultrasonic wave.
FIG. 42 is a side view of a conventional gas flowmeter. Device body 101 is configured by upper case 102 and lower case 103 which are formed by performing press working on metal. Inlet pipe 104 and outlet pipe 105 are disposed on upper case 102. Inlet pipe 104 opens in the inside of device body 101 through cut-off valve 106. Ultrasonic flow rate measuring unit 108 is connected to outlet pipe 105 through L-shaped connecting pipe 107.
However, in the conventional configuration, outlet pipe 105 supports ultrasonic flow rate measuring unit 108 in a cantilever manner. Accordingly, ultrasonic flow rate measuring unit 108 is supported in an unstable state. Particularly, the configuration is adopted where outlet pipe 105 supports ultrasonic flow rate measuring unit 108 approximately horizontally and hence, a moment applied to outlet pipe 105 becomes large thus bringing ultrasonic flow rate measuring unit 108 into a more unstable state. As a result, ultrasonic flow rate measuring unit 108 easily swings. This swinging of ultrasonic flow rate measuring unit 108 gives rise to a drawback that stable flow rate measurement cannot be performed.
To overcome this drawback, the configuration may be considered where connecting pipe 107 and ultrasonic flow rate measuring unit 108 are fixed to device body 101 by bolts. In such a configuration, device body 101 is formed by performing press working on metal. Accordingly, bolts penetrate device body 101. In this case, to prevent leakage of a gas through between the bolt and a periphery of a hole formed in device body 101, a sealing material is provided.
However, durability of the sealing material is not sufficient compared to a life of a gas meter. Accordingly, there is a drawback that leakage of a gas occurs between the bolt and the periphery of the hole formed in device body 101 when the sealing material is peeled off.